Photographic material for the direct production of positive photographic images



y is not reduced by the'developer. K formed at these areas, so that reduction of the silver 2,875,052 MATERIAL FOR THE DIRECT OF POSITIVE PHOTOGRAPHIC PHOTOGRAPHIC PRODUCTION IMAGES Edith Weyde, Leverkusen-Wiesdorf, Germany No Drawing. Original application August 6, 1949, Serial No. 109,0 73, now Patent No. 2,712,995, dated July 12, 1955. Drvidedand this application October 19, 1954, Serial No. 463,318

9 Claims. or. 96-68) This invention relates to a process for the direct production of positive photographic images and to photographic material used for such a process.

The present application is a division of my copending application'Serial No. 109,073, filed August 6, 1949, now U. S. Patent 2,712,995, granted July 12, 195 5.

It is known that photographic layers produced from silver chloride emulsions are blackened without previous exposure, in photographic developers that contain no potassium bromide. The reduction of silver chloride to silver is strongly inhibited by the addition of small amounts of potassium bromide to a developer (only a few mg./ltr. will do to bring about this effect). It has now been observed that sensitivity of this reaction can considerably be increased by adding to the silver chloride materials traces of such substances as act as nuclei for development, for instance, colloidal noble metals or noble metal compounds difiicultly soluble in water, as, for instance, colloidal silver, colloidal gold, silver sulfide etc. The quantities used thereof amount to about 0.0 l-0.5 g./ltr. of emulsion. If, besides traces of such substances as acting as nuclei for development, small amounts of a silver bromide emulsion of higher sensitivity are added to a silver chloride emulsion and the layers obtained are exposed according to the sensitivity of the silver bromide emulsion, on the subsequent development in a soda sulfite solution free from potassium bromide and containing developing substances, such as metol or hydroquinone, the following reaction takes place: the exposed silver bromide is reduced to silver, bromide ions corresponding to the amount of reduced silver being formed thereby. The bromide ions prevent the exposed areas from being fogged, i. e. they prevent a reduction of the silver chloride to silver. Silver bromide at the non-exposed areas No bromide ions are chloride proceeds smoothly. At the exposed areas therefore, only as much silver is formed as corresponds to the reduced bromide; as only very small amounts of silver are concerned, slight blackening only which is scarcely visible is produced, i. e. these areas after processing are practically white if the light-sensitive layer was cast onto paper, or they are transparent if the layer was cast onto a transparent base. At the non-exposed areas, however, silver chloride representing the chief constituent of the layers is reduced, so that these areas show a very deep blackening. So the exposed areas of these layers remain light whereas the non-exposed ones become dark, i. e. a direct positive image of the object is obtained by one process. In order to remove the non-developed silver halide, the developed images have still to be fixed, washed and dried. It is also feasible to modify the process in such a manner that the negative silver is removed by using known reducers so that positive silver only is left. This method allows one to obtain direct positives with excellent whites.

The proportion of silver chloride to silver bromide depends on the kind of emulsions used and lies in the range of between 0.1-10 grams of silver bromide to 100 grams of silver chloride. The preparation of these emulsion layers can also be performed in such a manner that by the 2,875,052 Patented Feb. 24, 1959 addition of small amounts of potassium bromide or potassium iodide to a silver chloride emulsion such direct positives yielding layers are obtained. The process, however, is not limited to mixtures of silver chloride and silver bromide. As low sensitive silver salts, besides silver chloride, other silver salts, such as silver oxalate, silver stearate, silver ferrocyanide etc., can be used in which case silver chloride may find application as the higher sensitive component. As higher sensitive silver salts, besides silver bromide, also silver iodide may be used. It is an essential feature of the new process that the photosensitive ingredient used in a small. amount exhibits a higher sensitivity to light and a lower solubility in the photographic developers used than the less. sensitive component. The process can also be modified in such a manner that the less sensitive and higher sensitive components of the mixture consist of mixtures of silver salt emulsions of different gradations. It is also possible to optically sensitize the more sensitive emulsion and to subsequently expose same behind a suitable light filter. Furthermore, known toning substances as well as'stabilizers, for instance, merca'pt-o benzothiazole, wetting agents etc., may be added to the layers thus obtained.

For achieving a good definition power of these photographic layers additions can be made to these layers to prevent or retard a diffusion of the dissolved silver salts. For this purpose there may be used, for instance, high molecular products, such as polyacrylic acid, polyvinyl alcohol, polyvinyl py rrolidone, and compounds containing long carbon chains, such as stearic acid residues. Also hardening of gelatin by means of well known products, for instance, formalin, shows a useful effect.

The composition of the developer solution has a considerable influence on the aforesaid process. These solutions are to develop the highersensitive ingredient before the lower sensitivity ingredient is dissolved and reduced. The same chemicals are used for such development which find application for the usual photographic processes, without potassium bromide however. For the silver chloride-silver bromide system the potassium bromide can be replaced by sodium chloride. Furthermore, for carrying out the new process, the presence of a silver halide solvent, for instance, sodium sulfite, i required. The silver halide dissolving effect of alkaline sulfite solutions can be increased by the addition of known compounds, for instance, sodium thiosulfate, organic amines etc. Also the developers employed for fine-grain development, for instance, p-pheriylene diamine and derivatives thereof, possess a sufiiciently strong dissolvingpower for silver chloride and other silver salts so that when using such substances the addition of further silver halide solvents can sometimes be dispensed with.

.Ithas been found that when using certain developing solutions the. addition of small amounts of potassium bromide generally not exceeding milligrams per litre has a useful effect, on development. Such addition, in comparison with the amounts of potassium bromide used in ordinary photographic developers, is so small that the developers used according to the present invention can be considered to be practically free from potassium bromide.

The process for the production of direct positive images according to the present invention shows the advantage that processing can be performed in the same way as in 'the case of a usual negative process without any additional processing steps. If the developer is appropriately composed .development proceeds extraordinarilyfast, an

advantage, for instance, for automatic photographic processes. The fact that the silver separated from the dissolved silver chloride is highly fine-grained and opaque allowsone to produce especially thin reverse layers with a very small amount of silver. A coating of less than 1 gram of silver per 111. is generally sufficient for this be subjected to any after-treatment known in photography,-

for instance, intensification, reduction, toning, etc. They may also be used for the contact hardening process and other processes known in the art. It is also feasible to modify the process in such a manner that the differently sensitive emulsions are cast in separate layers and the multilayer materials are worked up into direct positives by means of the above described developers.

Many specific objects, features and advantages of the present invention will become apparent to those skilled in the art from the specific examples appearing below. The following examples are not to be considered as limiting the invention but are merely illustrative of methods of carrying it out.

' Example 1 To a silver chloride emulsion prepared according to known methods are added per litre cc. of a silver bromide emulsion the sensitivity of which being about twice or three times as high as that of the silver chloride emulsion, and 0.1 gram of colloidal silver. The mixture of emulsions is cast as usual onto paper, film or glass, the silver content of the layer amounting to about 1 gram of silver per m After exposure development is performed in the following solution:

After 30 seconds of development a positive image of the object is obtained. As in the case of the usual photographic processes the developed positive is stopped in 2 percent acetic acid, fixed, washed, and dried. As sllver bromide emulsion any silver bromide emulsion prepared in the usual manner which is fit for the intended use may be employed. Sensitivity and gradation of the positives depend on the corresponding properties of the employed silver bromide emulsion. These layers generally exhibit a higher sensitivity to light than a negative prepared by means of a silver bromide emulsion only. Therefore, on using silver bromide emulsions of very high sensitivity to light for obtaining these mixed emulsions a material is obtained which is capable of recording extraordinarily weak actions of light.

Example 2 To a silver chloride emulsion prepared according to known processing methods are added per litre 20 cc. of a silver bromide emulsion the sensitivity of which being a hundred times higher than that of the silver chloride emulsion and 0.3 gram of colloidal gold. The mixture of these emulsions is applied in such a thin layer that the silver coating amounts to about 0.5 gram per m3 only. These layers can be hardened by adding formalin or other known substances and coated with a protective layer of gelatin to which, if desired, some colloidal silver is added. Development of this layer is carried out in the following solution:

After seconds of development a completely developed positive is obtained; owing to the very small coating thickness a fixing time of a few seconds will do. As the developing and fixing time can still essentially be shortened by raising the temperature of the solutions such layers are especially suited in combination with suitable apparatus for a fast production of direct positives.

Example 3 To a silver chloride emulsion of very low speed produced according to known recipes are added 500 cc. of a silver chloride-bromide emulsion of low sensitivity which has orthochromatically been sensitized with known dyestuffs, and 0.1 gram of colloidal silver. This emulsion is applied to paper as usual and developing is carried out in the following solution:

Water cc- 1000 Metol grams 3 Soda do Sodium sulfite anhydrous do.. Sodium chloride do 0.5 Temperature C 18 Example 4 To a silver chloride emulsion prepared according to well known processes are added per litre besides 0.2 gram of colloidal silver sulfide, 1 gram of potassium bromide or 1 gram of potassium iodide dissolved in water, a small amount of the silver chloride being converted thereby to silver bromide or silver iodide respectively. Such layers can be exposed as usual and a direct positive of brown image-color is obtained in a solution of the following composition:

Water cc 1000 p-Phenylenediamine "grams" 3 Soda do 5 Sodium sulfite anhydrous do 1 Temperature C 18 Developing time about m-inutes 24 Example 5 To 1000 parts of an emulsion of silver ferrocyanide, obtained by precipitating a silver nitrate solution with an equivalent amount of potassium ferrocyanide in the presence of gelatin, and exhibiting only a very low light sensitivity, are added per litre 20 cc. of a silver chloride emulsion and 0.3 gram of colloidal silver. These layers direct- 1y yield a positive on developing in the following solution:

Water cc 1000 Metol grams 2 Soda do 20 Sodium sulfite anhydrous do 10 Temperature C 18 Developing timeseconds In this way layers can be produced which possess a low light-sensitivity only.

Example 6 To a silver chloride emulsion prepared according to known processes are added per litre besides 0.02 gram of colloidal silver, 15 cc. of a fine-grained silver bromide emulsion the sensitivity of Which is 30 times as high as that of the silver chloride emulsion which has orthochromatically been sensitized as usual. In order to obtain layers with a high resolving power 5-10 grams of the sodium saltof Z-stearoylamino-5-7-disulfonic acid are added to the present invention the foregoing mixture. The emulsion is cast onto a sup port which is equipped with an antihalation layer in a rather small coating thickness. Development is carried through in the following solution:

Water cc 1000 Metol grams 0.5 Hydroquinone do 3 Soda do Sodium sulfite anhydrous do 10 Temperature C 18 Developing time about minute 1 In this way layers are obtained which are suitable for making reductions (microfilms).

The present invention for the production of direct positive images is not only suited for the processing methods as described in the Examples l-6 but may generally be employed wherever the production of photographic positives or duplicatenegatives is required. Whereas, for instance, accordingto the above described processing methods gelatin has been used as a binder, it is also feasible to modify the process in such a manner that other binding agents may find application, for instance, synthetic high molecular products such as sericose (partially hydrolyzed acetylcellulose), polyvinyl alcohol, hydroxy groups containing copolymerizates, collodium and other products used for this purpose in photography.

The new process may also be used for the production of printing matrices. A further field of application for is color photography, where it may be utilized, for instance, for the known methods according to the silver-bleach process, the process of color development, the toning process, for the screen plate, and other additive color processes, for the production of monochrome as well as of polychrome images. The various possibilities which are open to the new process shall be further explained in the following.

The new process has proved to be especially suitable for the direct production of photographic positive images when using other binding agents than gelatin. It is known that high sensitive silver bromide emulsions cannot easily be obtained in other binding agents than gelatin, for in stance, in synthetic high molecular products. 0n the other hand, however, it is comparatively easy to produce silver chloride emulsions or other silver salts emulsions of comparatively low sensitivity by means of such binding agents. As according to the new process for the direct production of positive images, besides themain portion of silver chloride only very small amounts of a high sensitive silver bromide emulsion are required, these small amounts of a high sensitive silver bromide emulsion prepared as known in the art. by means of gelatin as binding agent can be added to a silver chloride emulsion precipitated in any synthetic high molecular compound which is suited for photographic processes, for instance, sericose, polyvinyl alcohol etc. The gelatin containing emulsion is preferably diluted with water or with another solvent, for instance, acetone-water-mixture. Such layers give sensitivities which are essentially higher than those of the hitherto known emulsions on the base of non-gelatinous binding agents. If emulsions of lower sensitivity are to be obtained it may be of advantage to precipitate also the higher sensitive emulsions, for instance, the silver bromide emulsion in another binding agent. The following example serves for illustrating this process:

Example 7 10 grams of silver nitrate dissolved in a mixture of acetone and water 1:1) and subsequently 3.5 parts of sodium chloride dissolved in cc. of water are added to 1000 parts of a 4 percent sericose solution in acetonewater (2:1) (sericose=partly hydrolyzed acetyl cellu lose), a finely grained silver chloride precipitate being printing matrices according to the tivity of the silver bromide emulsion is: developed at atemperature of 18 C. for 30 seconds in the following solution:

Water cc 1000 Metol g ams..- 2 Sodium sulfite anhydrous do 30 Soda sicc ..do...... 25

If the new process is to be used for the production of photographic positives which are to be used as printing matrices, the following possibilities are given: Small amounts of a higher sensitive silver bromide emulsion and traces of colloidal silver sulfide as developing nuclei are added, for instance, to a silver chloride emulsion of comparatively low sensitivity and the layer thus obtained is developed after exposing in a developer which is free from potassium bromide, a direct positive being obtained thereby. The gelatin of this positive can be tanned at the silver-containing places with a solution of bichromate and can thus be rendered absorbable for fat-soluble colours. The layer can also be hardened by development in a sulfite-free pyrocatechol developer and the non-hardened gelatin can be washed oil with hot water. For the latter process no sulfite as a silver chloride solvent must be added to the developer as this would prevent the hardening, but in this case sodium thiosulfate or other solvents, for instance, ammonium salts or organic amines, are same principle also wash-out reliefs With dyed layers can be produced for monochrome or polychrome images. The following example is to illustrate the production of new invention.

Example 8 Water cc 1000 Metol .grams 2 Soda do 30 Sodium sulfite anhydrous do 25 Temperature 0.. 18 Developing time seconds. 40

The positive thus obtained is fixed, washed and converted in the following solution into a printing relief:

Water cc 1000 Potassium bichromate grams 5 Copper sulfate do 15 Potassium bromide do 10 used. According to the latter prevent at these layer material. To this emulsion are added in the usual manner small amounts of such products that act as developing nuclei, for instance, colloidal silver, colloidal gold etc. and a colorformer which is fast to diffusion. Such color formers for the chromogen development have been disclosed in patents. For this purpose, for instance, components of azomethineor indophenol dyestuifs may be used which carry solubilizing acid groups and residues of higher aliphatic hydrocarbons, of natural resins, of polypeptides or hydroaromatic hydrocarbons etc. These emulsions are cast in the usual manner in superposed layers, interposing a yellow filter between the upper, only blue-sensitive layer and the lower greenand redsensitive layers. After appropriate exposure adapted to the sensitivity of the silver bromide emulsion these layers are treated in a developer containing, for instance, p-phenylene diamine or its derivatives which, with the color couplers contained in the layers, yields a dyestufi. These substances have the property to dissolve silver chloride to a considerable extent so that only very small amounts of sodium sulfite need to be added to these developers in order to initiate a direct positive development. The color-forming developer reduces the exposed silver bromide, bromide ions being set free thereby. The places a reduction of the dissolved silver chloride which, therefore, is reduced to silver only at the non-exposed places, the corresponding dyestuffs being simultaneously formed thereby. Whereas the developing substances suitable for the present invention reduce silver chloride very fast, this process proceeds considerably more difficultly and slowly in the case of silver bromide. If, therefore, very small amounts of another developing substance of higher reducing power which is not suitable for color formation, for instance metol, are added to such a color-forming developer, reduction of silver bromide is essentially due to this substance; in this case, no oxidation product is formed which with the color coupler present in the layer would give a dyestuff, i. e. the weak negative resulting from the silver bromide consists of silver only and contains no dyestuif. On the other hand, reduction of silver chloride which is present in much bigger quantities is essentially due to the colorforming developer the oxida-- tion product of which gives the dyestuffs desired with the color couplers. After developing and intermediately washing the small amounts of negative silver and the larger amounts of silver formed by the reduction of silver chloride are dissolved by means of known products, for instance, potassium ferricyanide, or converted into silver salts which are removed by subsequent fixations. The process is suited for the production of high sensitive, negative as well as positive photographic material. The following example shall further illustrate this process.

Example 9 To a silver chloride emulsion prepared as known in the art are added per litre 0.1 gram of colloidal silver and 12 cc. of a higher sensitive silver bromide emulsion which is sensitized with known dyestuifs for the redor CHa.N. OrlHsu OH NH.CO

is first coated onto paper, glass or film. Upon this layer a there is coated the corresponding green-sensitive emulsion After coating a yellow filter layer prepared as known in the art as intermediate layer a merely blue-sensitive emulsion mixture is used for providing the upper layer. To this emulsion mixture are added per litre 20 grams of a compound of the following formula:

(IJOOH ooorl which on development gives a yellow dyestuff. After exposure these layers are treated at 18 C. for 40 seconds in the following developer:

The further processing of the images is done as known in the art. Apositive three-color image is thus obtained.

What I claim is:

1. Photographic light sensitive layers comprising in contact with each other, a silver salt emulsion of low light sensitivity, the silver salt of which is a salt selected from the group consisting of silver chloride, silver ferrocyanide and organic silver salts, and a second silver salt emulsion of substantially higher light sensitivity than said first silver salt emulsion, the silver salt of said second emulsion being a salt of the group consisting of silver bromide, silver iodide, silver chloride and a mixture of silver bromide and silver chloride, said silver salt of said second emulsion being present in amounts of from 0.1 to 10% by weight based on the weight of the silver salt of said first emulsion, the silver salts of each emulsion being developable with the same developer, the silver salt of the second emulsion being less soluble in the developer, and that of the first emulsion being spontaneously developable without exposure to light.

2. Photographic light sensitive layersaccording to claim 1, wherein the two light sensitive silver salt emulsions are mixed with each other.

3. Photographic light sensitive layers according to claim 1, wherein the two silver salt emulsions are present in different supercoated layers.

4. Photographic light sensitive layers according to claim 1, wherein said first silver salt emulsion is a silver chloride emulsion and said second silver salt emulsion is a silver bromide emulsion.

5. Photographic light sensitive layers according to claim 1, wherein said first silver salt emulsion contains development nuclei.

6. Photographic light sensitive layers according to claim 5, where the development nuclei are selected from the group consisting of colloidal noble metals selected from the group consisting of gold, silver and platinum and colloidal compounds of said same metals, said compounds being substantially insoluble in water.

7. Photographic light sensitive layer according to claim 1, in which the silver salts of both said emulsions contain not more than 1 gram of silver per square meter. 8. Photographic light sensitive layers according to claim 1 wherein the silver salt of said first emulsion is silver ferrocyanide and the silver salt of said second emulsion is silver chloride.

9. Photographic light sensitive layers according to claim 1 wherein the silver salt of said first emulsion is an organic silver salt and the silver salt of said second 10 emulsion is silver chloride.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES British Journal of Photography, June 5, 1914, page 446. 

